Pump driving method and device therefor

ABSTRACT

A pump driving apparatus has a characteristic changing section which receives a set pressure, a set flowing amount, a set horse power, and a DC voltage of the converter section as input, outputs modified values of pressure, flowing amount, and horse power, and supplies the modified values to the horse power command generation section. Therefore, the motor can be driven to suit the change in power voltage so that the motor capacity can be utilized sufficiently.

TECHNICAL FIELD

The present invention relates to a pump driving method and apparatusthereof which drive a motor based upon a command value using dischargepressure—discharge flow characteristic and carrying out feedback of thedischarge pressure, and drive a pump using the motor.

BACKGROUND ART

From the past, a pump driving apparatus is proposed which drives a motorbased upon a command value using discharge pressure—discharge flowcharacteristic and carrying out feedback of the discharge pressure, anddrives a pump using the motor.

FIG. 1 is a block diagram illustrating a conventional pump drivingapparatus.

The pump driving apparatus comprises a converter section 101, aninverter section 102, a motor 103, and a pump 104.

The converter section 101 receives an alternate current power source asinput and generates a direct current voltage.

The inverter section 102 receives the direct current voltage as inputand outputs an alternate current voltage.

The motor 103 is supplied the alternate current voltage.

The pump 104 is connected to an output shaft of the motor 103.

The pump driving apparatus also comprises a horse power commandgeneration section 105, a subtraction section 106, a proportionalcontroller 107, an integral controller 108, an integrator 109, anaddition section 110, a speed control section 111, and a current controlsection 112.

The horse power command generation section 105 generates a horse powercommand based upon discharge pressure—discharge flow characteristic(hereinafter, referred to as P-Q characteristic), a current pressure,and a current flowing amount, the P-Q characteristic being generated, asis illustrated in FIG. 5, by a set pressure, a set flowing amount, and aset horse power defined for a predetermined power voltage.

The subtraction section 106 calculates a difference between the horsepower command output from the horse power command generation section 105and a current horse power.

The proportional controller 107 receives the horse power difference asinput, and carries out the proportional control.

The integral controller 108 receives the horse power difference asinput, and carries out the integral control.

The integrator 109 integrates the integral control result.

The addition section 110 adds the proportional control result and theintegration result so as to obtain a proportion-integration controlresult (speed command).

The speed control section 111 receives the speed command as input,carries out the speed control operation, and outputs a current command.

The current control section 112 receives the current command and a DCvoltage of the converter section 101, carries out the current controloperation so as to generate a duty command, and supplies the dutycommand to the inverter section 102.

The pump driving apparatus further comprises a speed detection section114, a flowing amount detection section 117, a pressure sensor 115, anda horse power operation section 116.

The speed detection section 114 receives a pulse output from a pulsegenerator 113 which is connected to the motor 103, and calculates acurrent speed of the motor 103 based upon a pulse interval.

The flowing amount detection section 117 receives the current speed asinput, and calculates a discharge flow by taking a pump volume and thelike into consideration.

The pressure sensor 115 detects a current pressure of discharge fluidfrom the pump 104.

The horse power operation section 116 calculates a current horse powerbased upon the current flowing amount and the current pressure.

Therefore, adequate pump control can be realized in which the definedP-Q characteristic is determined to be a maximum area.

However, a power voltage is not guaranteed to be kept to a predeterminedvoltage. A power voltage affects driving, stopping, and the like ofadjacent apparatus and the like, and varies accordingly. Therefore,sufficient capacity cannot be realized when a pump is driven using P-Qcharacteristic which is defined for the predetermined power voltage.

Description is made further.

When a power voltage becomes lower than a predetermined rated voltage, adischarge pressure which is actually possible to be output becomes lowerthan the discharge pressure {circumflex over (1)} for the predeterminedrated voltage, as is illustrated with {circumflex over (3)} in FIG. 2.This P-Q characteristic can be converted to torque—revolution speedcharacteristic of a motor (refer to FIG. 3). And, {circumflex over(1)}{circumflex over (2)}{circumflex over (3)} in FIG. 2 correspond to{circumflex over (1)}{circumflex over (2)}{circumflex over (3)} in FIG.3, respectively. As a result, a condition continues where a currentvalue does not reach for the command value corresponding to the P-Qcharacteristic illustrated with {circumflex over (1)}. And, for thistime period, the integrator 109 of the PQ control continues theintegration, therefore, the discharge pressure greatly overshoots afterthe integration result exceeding the constant horse power region (windupphenomenon).

Therefore, in the past, the P-Q characteristic is determined, as isillustrated with {circumflex over (3)}, for not causing problem incontrol response even when a power voltage is lowered to some degree. Asa result, a disadvantage arises in that a motor capacity cannot beutilized sufficiently.

On the contrary, when the discharge pressure which is actually possibleto be output becomes higher than the discharge pressure {circumflex over(1)} for the predetermined rated voltage, as is illustrated with{circumflex over (2)} in FIG. 2, the output following the P-Qcharacteristic illustrated with {circumflex over (2)} becomes possible.However, a command value only corresponds to the P-Q characteristicillustrated with {circumflex over (1)}, therefore, a disadvantage arisesin that a motor capacity cannot be utilized sufficiently, similarly.

SUMMARY OF THE INVENTION

The present invention was made in view of the above problems.

It is an object of the present invention to provide a pump drivingmethod and apparatus thereof in which a motor capacity cannot beutilized sufficiently following varying in a power voltage.

A pump driving method of a first aspect changes dischargepressure—discharge flow characteristic in correspondence with a powervoltage when a motor is driven based upon a command value usingdischarge pressure—discharge flow characteristic and feedback of thedischarge pressure is carried out, and a pump is driven using the motor.

A pump driving method of a second aspect holds dischargepressure—discharge flow characteristics corresponding to a plurality ofpower voltage, respectively, and selects a corresponding dischargepressure—discharge flow characteristic in correspondence with adetection value in power voltage.

A pump driving method of a third aspect defines a predeterminedpressure, flowing amount, and horse power as characteristic values for apredetermined power voltage, and changes a discharge pressure—dischargeflow characteristic in correspondence with a detection value in powervoltage.

A pump driving method of a fourth aspect judges whether or not a DCvoltage of an inverter for supplying a driving voltage to a motor is aideal DC voltage value of an alternate current power voltage, changes adischarge pressure—discharge flow characteristic for the DC voltage whenit is judged that the DC voltage is the ideal DC voltage value of thealternate current power voltage, and maintains the changed dischargepressure—discharge flow characteristic when it is judged that the DCvoltage is not the ideal DC voltage value of the alternate current powervoltage and when the just prior DC voltage is the ideal DC voltage valueof the alternate current power voltage, when a motor is driven basedupon a command value using discharge pressure—discharge flowcharacteristic and feedback of the discharge pressure is carried out,and a pump is driven using the motor.

A pump driving method of a fifth aspect maintains a power voltage valueinstead the maintaining of the discharge pressure—discharge flowcharacteristic.

A pump driving apparatus of a sixth aspect drives a motor based upon acommand value using discharge pressure—discharge flow characteristic andcarries out feedback of the discharge pressure, and drives a pump usingthe motor, the apparatus comprises characteristic changing means forchanging discharge pressure—discharge flow characteristic incorrespondence with a power voltage.

A pump driving apparatus of a seventh aspect employs means for holdingdischarge pressure—discharge flow characteristics corresponding to aplurality of power voltage, respectively, and for selecting acorresponding discharge pressure—discharge flow characteristic incorrespondence with a detection value in power voltage, as thecharacteristic changing means.

A pump driving apparatus of an eighth aspect employs means for defininga predetermined pressure, flowing amount, and horse power ascharacteristic values for a predetermined power voltage, and forchanging a discharge pressure—discharge flow characteristic incorrespondence with a detection value in power voltage, as thecharacteristic changing means.

A pump driving apparatus of a ninth aspect drives a motor based upon acommand value using discharge pressure—discharge flow characteristic andcarries out feedback of the discharge pressure, and drives a pump usingthe motor, the apparatus comprises judgment means for judging whether ornot a DC voltage of an inverter for supplying a driving voltage to amotor is a ideal DC voltage value of an alternate current power voltage,for changing a discharge pressure—discharge flow characteristic for theDC voltage when it is judged that the DC voltage is the ideal DC voltagevalue of the alternate current power voltage, and for maintaining thechanged discharge pressure—discharge flow characteristic when it isjudged that the DC voltage is not the ideal DC voltage value of thealternate current power voltage and when the just prior DC voltage isthe ideal DC voltage value of the alternate current power voltage, whena motor is driven based upon a command value using dischargepressure—discharge flow characteristic and feedback of the dischargepressure is carried out, and a pump is driven using the motor.

A pump driving apparatus of a tenth aspect employs means for maintaininga power voltage value instead the maintaining of the dischargepressure—discharge flow characteristic, as the judgment means.

When the pump driving method of a first aspect is employed, thedischarge pressure—discharge flow characteristic is changed incorrespondence with a power voltage when a motor is driven based upon acommand value using discharge pressure—discharge flow characteristic andfeedback of the discharge pressure is carried out, and a pump is drivenusing the motor. Therefore, the motor can be driven to match a valuewhich can be actually output, and the motor capacity can be made thebest use of sufficiently.

When the pump driving method of a second aspect is employed, thedischarge pressure—discharge flow characteristics corresponding to aplurality of power voltage are held, respectively, and a correspondingdischarge pressure—discharge flow characteristic is selected incorrespondence with a detection value in power voltage. Therefore,performing of the processing rapidly can be realized, and operation andeffect similar to those of the first aspect can be realized.

When the pump driving method of a third aspect is employed, apredetermined pressure, flowing amount, and horse power are defined ascharacteristic values for a predetermined power voltage, and a dischargepressure—discharge flow characteristic is changed in correspondence witha detection value in power voltage. Therefore, a required memorycapacity can be made smaller, and operation and effect similar to thoseof the first aspect can be realized.

When the pump driving method of a fourth aspect is employed, it isjudged whether or not a DC voltage of an inverter for supplying adriving voltage to a motor is a ideal DC voltage value of an alternatecurrent power voltage, a discharge pressure—discharge flowcharacteristic is changed for the DC voltage when it is judged that theDC voltage is the ideal DC voltage value of the alternate current powervoltage, and the changed discharge pressure—discharge flowcharacteristic is maintained when it is judged that the DC voltage isnot the ideal DC voltage value of the alternate current power voltageand when the just prior DC voltage is the ideal DC voltage value of thealternate current power voltage, when a motor is driven based upon acommand value using discharge pressure—discharge flow characteristic andfeedback of the discharge pressure is carried out, and a pump is drivenusing the motor. Therefore, instability in transition condition isdissolved, the motor can be driven to match a value which can beactually output, and the motor capacity can be made the best use ofsufficiently.

When the pump driving method of a fifth aspect is employed, a powervoltage value is maintained instead the maintaining of the dischargepressure—discharge flow characteristic. Therefore, held data amount canbe made smaller, and operation and effect similar to those of the fourthaspect can be realized.

When the pump driving apparatus of a sixth aspect is employed, thedischarge pressure—discharge flow characteristic is changed incorrespondence with a power voltage by the characteristic changing meanswhen a motor is driven based upon a command value using dischargepressure—discharge flow characteristic and feedback of the dischargepressure is carried out, and a pump is driven using the motor.Therefore, the motor can be driven to match a value which can beactually output, and the motor capacity can be made the best use ofsufficiently.

When the pump driving apparatus of a seventh aspect is employed, meansfor holding discharge pressure—discharge flow characteristicscorresponding to a plurality of power voltage, respectively, and forselecting a corresponding discharge pressure—discharge flowcharacteristic in correspondence with a detection value in powervoltage, is employed as the characteristic changing means. Therefore,performing of the processing rapidly can be realized, and operation andeffect similar to those of the sixth aspect can be realized.

When the pump driving apparatus of an eighth aspect is employed, meansfor defining a predetermined pressure, flowing amount, and horse poweras characteristic values for a predetermined power voltage, and forchanging a discharge pressure—discharge flow characteristic incorrespondence with a detection value in power voltage, is employed asthe characteristic changing means. Therefore, a required memory capacitycan be made smaller, and operation and effect similar to those of thesixth aspect can be realized.

When the pump driving apparatus of a ninth aspect is employed, it isjudged whether or not a DC voltage of an inverter for supplying adriving voltage to a motor is a ideal DC voltage value of an alternatecurrent power voltage, a discharge pressure—discharge flowcharacteristic is changed for the DC voltage when it is judged that theDC voltage is the ideal DC voltage value of the alternate current powervoltage, and the changed discharge pressure—discharge flowcharacteristic is maintained when it is judged that the DC voltage isnot the ideal DC voltage value of the alternate current power voltageand when the just prior DC voltage is the ideal DC voltage value of thealternate current power voltage, by the judgment means, when a motor isdriven based upon a command value using discharge pressure—dischargeflow characteristic and feedback of the discharge pressure is carriedout, and a pump is driven using the motor. Therefore, instability intransition condition is dissolved, the motor can be driven to match avalue which can be actually output, and the motor capacity can be madethe best use of sufficiently.

When the pump driving apparatus of a tenth aspect is employed, means formaintaining a power voltage value instead the maintaining of thedischarge pressure—discharge flow characteristic, is employed as thejudgment means. Therefore, held data amount can be made smaller, andoperation and effect similar to those of the ninth aspect can berealized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a conventional pump drivingapparatus;

FIG. 2 is a diagram illustrating P-Q characteristic;

FIG. 3 is a diagram illustrating torque—revolution speed characteristicin correspondence with the P-Q characteristic of FIG. 2;

FIG. 4 is a block diagram illustrating a pump driving apparatus of anembodiment according to the present invention;

FIG. 5 is a diagram useful in understanding generation of P-Qcharacteristic;

FIG. 6 is a block diagram illustrating a main portion of the pumpdriving apparatus of the embodiment according to the present invention;

FIG. 7 is a block diagram illustrating a main portion of a pump drivingapparatus of another embodiment according to the present invention; and

FIG. 8 is a block diagram illustrating a main portion of a pump drivingapparatus of a further embodiment according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, referring to the attached drawings, we explain embodimentsof a pump driving method and apparatus thereof according to the presentinvention.

FIG. 4 is a block diagram illustrating a pump driving apparatus of anembodiment according to the present invention.

FIG. 6 is a block diagram illustrating a characteristic changing section18 of FIG. 4 in more detail.

The pump driving apparatus comprises a converter section 1, an invertersection 2, a motor 3, and a pump 4.

The converter section 1 receives an alternate current power source asinput and generates a direct current voltage.

The inverter section 2 receives the direct current voltage as input andoutputs an alternate current voltage.

The motor 3 is supplied the alternate current voltage.

The pump 4 is connected to an output shaft of the motor 3.

The pump driving apparatus also comprises a characteristic changingsection 18, a horse power command generation section 5, a subtractionsection 6, a proportional controller 7, an integral controller 8, anintegrator 9, an addition section 10, a speed control section 11, and acurrent control section 12.

The characteristic changing section 18 receives a set pressure, a setflowing amount, a set horse power, and a DC voltage of the convertersection 1 as input, outputs modified values of pressure, flowing amount,and horse power, and supplies the modified values to the horse powercommand generation section 5.

The horse power command generation section 5 calculates a horse powercommand based upon the modified values of pressure, flowing amount, andhorse power, and current pressure, and current flowing amount.

The subtraction section 6 calculates a difference between the horsepower command output from the horse power generation section 5 and acurrent horse power.

The proportional controller 7 receives the horse power difference asinput, and carries out the proportional control.

The integral controller 8 receives the horse power difference as input,and carries out the integral control.

The integrator 9 integrates the integral control result.

The addition section 10 adds the proportional control result and theintegration result so as to obtain a poroportion-integration controlresult (speed command).

The speed control section 11 receives the speed command as input,carries out the speed control operation, and outputs a current command.

The current control section 12 receives the current command and a DCvoltage of the converter section 1, carries out the current controloperation so as to generate a duty command, and supplies the dutycommand to the inverter section 2.

The pump driving apparatus further comprises a speed detection section14, a flowing amount detection section 17, a pressure sensor 15, and ahorse power operation section 16.

The speed detection section 14 receives a pulse output from a pulsegenerator 13 which is connected to the motor 3, and calculates a currentspeed of the motor 3 based upon a pulse interval.

The flowing amount detection section 17 receives the current speed asinput, and calculates a discharge flow by taking a pump volume and thelike into consideration.

The pressure sensor 15 detects a current pressure of discharge fluidfrom the pump 4.

The horse power operation section 16 calculates a current horse powerbased upon the current flowing amount and the current pressure.

The pump driving apparatus further comprises a ratio calculation section27, and a multiplication section 28.

The ratio calculation section 27 calculates a ratio between apredetermined power voltage 26 and the DC voltage of the convertersection 1.

The multiplication section 28 multiplies the operation result (voltagechange ratio) calculated by the ratio calculation section 27 to the sethorse power so as to generate the modified horse power.

Operation of the pump driving apparatus having the above arrangement isas follows.

Operation in a case where the predetermined voltage is equal to thepredetermined power voltage is similar to that of the pump drivingapparatus in FIG. 1, therefore, description for the case is omitted.Only operation in a case where the power voltage is changed, isdescribed.

When a power voltage is different from the predetermined power voltage,the DC voltage output from the converter section I changes incorrespondence with the changing of the power voltage.

The characteristic changing section 18 supplies modified values(pressure, flowing amount, horse power) to the horse power commandgeneration section 5 in correspondence with the DC voltage, even whenthe set pressure, the set flowing amount, and the set horse power areconstant.

As a result, the horse power command generation section 5 generates ahorse power command based upon the adequate P-Q characteristic, and thepump 4 is driven based upon the generated horse power command. In otherwords, the motor can be driven to suit a value which can actually beoutput so that the motor capacity can be utilized sufficiently.

It is preferable that the horse power command generation section 5generates characteristic for every region a, b, and c illustrated inFIG. 5, based upon the modified pressure, flowing amount, and horsepower.

In the above embodiment, P-Q characteristic is changed using the DCvoltage. However, it is possible that P-Q characteristic is changedusing an AC power voltage. When AC power is three phase power, it isrequired to detect power voltages for three phases to deal with theunbalanced supply voltage. Therefore, it is preferable that the DCvoltage is used in view of simplification in arrangement, and reductionin cost.

FIG. 7 is a block diagram illustrating a main portion of acharacteristic changing section 18 of a pump driving apparatus ofanother embodiment according to the present invention.

The characteristic changing section in FIG. 7 comprises a low-passfilter 222, a driving condition stability judgment section 223, a ratiocalculation section 227, and a multiplication section 228.

The low-pass filter 222 removes high frequency noises and the likeincluded in the input DC voltage.

The driving condition stability judgment section 223 judges whether ornot driving condition is stable. The ratio calculation section 227calculates a ratio between the output voltage from the low-pass filter222 and the predetermined power voltage output from a predeterminedpower voltage holding section 226.

The multiplication section 228 multiplies the operation result (voltagechange ratio) calculated by the ratio calculation section 227 to the sethorse power so as to generate a modified horse power.

A section for judging that driving condition is stable, for example,when a condition is continuing equal to or more than 500 msec, in thecondition the motor 3 is driven equal to or less than 2000 rpm and whenspeed change under the condition is equal to or less than 500 rpm, orwhen a condition is continuing equal to or more than 500 msec, in thecondition the motor 3 is driven equal to or less than 2000 rpm and whenspeed change under the condition exceeds 500 rpm and when the motor 3 isdriven equal to or less than 2000 rpm after 500 msec has passed, isemployed as the driving condition stability judgment section 223.However, it is possible to employ other conditions.

When the arrangement in FIG. 7 is employed, only when it is judged thatdriving condition is stable, a switch 224 is turned on so as tosample-hold the corrected set horse power which is the output value ofthe multiplication section 228, and to hold the corrected set horsepower in a modified horse power holding section 225. When it is judgedthat driving condition is not stable, the switch 224 is turned off so asto generate a modified horse power which is held by the modified horsepower holding section 225.

Therefore, driving of the pump with more stability is realized.

Description is made further.

When the power voltage is detected from the DC voltage, for example,power regeneration may be generated due to deceleration of the motor sothat the DC voltage may be raised temporally. When P-Q characteristic ischanged by taking the DC voltage into consideration as power voltagechange directly for such case, the control condition may becomeunstable.

However, when the arrangement of FIG. 7 is employed, the motor 3continues power running for some time period depending upon the motorspeed and the degree of power voltage change so that the power isconsumed, the power corresponding to the raise due to the powerregeneration. The correction of P-Q characteristic is carried out onlyin a case that the DC voltage is supposed to become the ideal DC voltagevalue of the AC power voltage (AC voltage×2^(1/2)). In transient state,the modified horse power is continuously used, the modified horse powerbeing held by the modified horse power holding section 225 prior tobecoming transient state. Consequently, the pump 4 can be controlledstably.

By employing a section for judging that driving condition is stable, forexample, when a condition is continuing equal to or more than 500 msec,in the condition the motor 3 is driven equal to or less than 2000 rpmand when speed change under the condition is equal to or less than 500rpm, or when a condition is continuing equal to or more than 500 msec,in the condition the motor 3 is driven equal to or less than 2000 rpmand when speed change under the condition exceeds 500 rpm and when themotor 3 is driven equal to or less than 2000 rpm after 500 msec haspassed, as the driving condition stability judgment section 223, it ispossible that P-Q characteristic is corrected only in dwellingcondition.

When the AC power voltage is directly detected, the above disadvantagesand the like are not generated. Therefore, it is not necessary that thearrangement of FIG. 7 is employed.

By allowing the current voltage holding section 325 to hold the outputvoltage from the low-pass filter 322 by turning the switch 325 on/offusing the output of the driving condition stability judgment section323, as is illustrated in FIG. 8, operation and effect similar to thoseof FIG. 7 can be realized.

1. A pump driving method comprising: driving a motor based upon acommand value using a discharge pressure—discharge flow characteristic;carrying out feedback control of a discharge pressure, and driving apump using the motor to change the discharge pressure—discharge flowcharacteristic in correspondence with a power voltage.
 2. A pump drivingmethod as set forth in claim 1, further comprising holding, thedischarge pressure—discharge flow characteristics corresponding to aplurality of power voltage, respectively, and selecting a correspondingone of the discharge pressure—discharge flow characteristics incorrespondence with a detection value of the power voltage.
 3. A pumpdriving method as set forth in claim 1, further comprising defining apredetermined pressure, flowing amount, and horse power ascharacteristic values for a predetermined power voltage, and changingthe discharge pressure—discharge flow characteristic in correspondencewith a detection value of the power voltage.
 4. A pump driving methodcomprising: driving a motor based upon a command value using dischargepressure—discharge flow characteristic, carrying out feedback control ofa discharge pressure, driving a pump using the motor based on whether ornot a DC voltage of an inverter for supplying a driving voltage to themotor is an ideal DC voltage value of an alternate current powervoltage, changing the discharge pressure—discharge flow characteristicfor the DC voltage upon judging that the DC voltage is the ideal DCvoltage value of the alternate current power voltage, and maintaining achanged discharge pressure—discharge flow characteristic upon judgingthat the DC voltage is not the ideal DC voltage value of the alternatecurrent power voltage and when just previously judged the DC voltage wasthe ideal DC voltage value of the alternate current power voltage. 5.The pump driving method as set forth in claim 4, wherein the maintainingof the changed discharge pressure—discharge flow characteristic isaccomplished by maintaining a power voltage value instead themaintaining of the discharge pressure—discharge flow characteristic. 6.A pump driving apparatus comprising: a motor configured to be drivenbased upon a command value using a discharge pressure—discharge flowcharacteristic to feedback control a discharge pressure, a pumpoperatively coupled to the motor, and a characteristic changing sectionconfigured to change the discharge pressure—discharge flowcharacteristic in correspondence with a power voltage.
 7. The pumpdriving apparatus as set forth in claim 6, wherein the characteristicchanging section is configured to hold the discharge pressure—dischargeflow characteristics corresponding to a plurality of power voltage,respectively, and to select a corresponding one of the dischargepressure—discharge flow characteristics in correspondence with adetection value of the power voltage.
 8. The pump driving apparatus asset forth in claim 6, wherein the characteristic changing section isconfigured to define a predetermined pressure, flowing amount, and horsepower as characteristic values for a predetermined power voltage, and tochange the discharge pressure—discharge flow characteristic incorrespondence with a detection value of the power voltage.
 9. A pumpdriving apparatus comprising: a motor configured to be driven based upona command value using a discharge pressure—discharge flow characteristicto feedback control a discharge pressure, a pump operatively coupled tothe motor, and judgment means for judging whether or not a DC voltage ofan inverter for supplying a driving voltage to a motor is an ideal DCvoltage value of an alternate current power voltage, for changing adischarge pressure—discharge flow characteristic for the DC voltage whenit is judged that the DC voltage is the ideal DC voltage value of thealternate current power voltage, and for maintaining the changeddischarge pressure—discharge flow characteristic upon judging that theDC voltage is not the ideal DC voltage value of the alternate currentpower voltage and when the just previously judged the DC voltage was theideal DC voltage value of the alternate current power voltage.
 10. The Apump driving apparatus as set forth in claim 9, wherein the judgmentmeans maintains a power voltage value instead the maintaining of thedischarge pressure—discharge flow characteristic.